In the manufacture of electronic devices, it is frequently desirable to combine two components--a substrate, which may, for example, be an integrated circuit (IC) chip or a chip carrier, and a number of leads that create connections between the substrate and the surrounding electronic circuitry. The leads are connected to the substrate at its contact pads, which are exposed electrically conductive areas, usually at an edge or periphery of one face of the substrate.
The speed at which the leads are attached to the substrate is a paramount consideration in the manufacturing process, as higher throughput and thus lower costs can provide the economy needed for successfully meeting competition. Technologies have been designed to attempt to speed the process. A process in common use includes forming a frame or strip with a number of individual leads spaced to correspond to contact pads on the substrate. Solder is then applied to the contact pads on the substrate or the leads. The frame or strip is positioned adjacent the substrate, putting the leads in juxtaposition or direct contact with respective contact pads. In order to hold the leads in contact with their pads during soldering, the substrate is pressed onto the leads. Unfortunately, this can sometimes crack the substrate, which renders it unusable. While being held under pressure, the frame/substrate assembly is heated, causing the solder to melt and, upon cooling, creates an electrical and physical connection between the leads and the substrate.
Typically, heat is applied to the underside of the leads for three to four seconds, melting the solder, which flows between the contact pads and the leads. To prevent movement of the leads while the solder remains in a liquid state, which could result in misalignment and misconnection of the leads, a support and clamp remain in position, holding the components in place until the solder has sufficiently cooled. Typically, this may take about: fifteen seconds. Overall, this process requires that a particular lead frame and substrate remain at the soldering station for about 20 seconds.
After soldering is completed, the lead frame is cut away, leaving the ends of the leads extending from the periphery of the substrate, ready for connection to surrounding electronic devices. A similar procedure is used for a linear strip array of leads.
The time required at the soldering station for each substrate makes the manufacturing speed and thus the throughput undesirably low for competitive production. Also, the substantial risk of cracking a substrate and having to completely discard the unit adds to the costs involved.
Thus, it is an object of the invention to provide a lead arrangement (which may be in the form of a frame or strip) that decreases the time the frame or strip and substrate must remain at a soldering station.
It is another object of the invention to provide a lead arrangement that includes means for retaining a substrate against the leads while the solder cools, without risk of damaging the substrate.
It is a further object of the invention to provide a lead arrangement including means for retaining a substrate against the leads during soldering, where the retaining means is formed integrally with the leads and is readily removed at the end of the manufacturing process.
It is yet another object of the invention to provide a lead arrangement that is economical to fabricate and produces significant savings in applying leads to substrates, in decreased time.